What is “The requested URL / was not found on this server”?
This error normally happens after the installation of your Magento website. When it happens, you’ll see the Not Found page with the message “The requested URL /…/… was not found on this server” on any URL on your website.
even the admin URL
But if you include “index.php” in the URLs, they are accessible again:
Why does this happen?
This is a problem from Apache server when it is unable to process links without “index.php”.
How to solve it?
You need to setup your Magento so that all links point to index.php file.
By default, this file is included in Magento installation: https://github.com/magento/magento2/blob/2.2-develop/.htaccess.sample which already has a configuration part for Apache
To use the Apache configuration form this file, backup the existing .htaccess file in your website, then rename the file .htaccess.sample into .htaccess.
That’s it! Now you can refresh your website to see the result.